The present invention relates to a shut-down device for a diesel engine, and more particularly relates to a device for stopping a diesel engine by cutting the fuel supply or the intake air supply when an engine stopping command is given.
Some methods have been formerly proposed in order to stop diesel engines. One method is to cut the fuel supply by a stop lever or to stop the intake air supply by shutting a valve provided on an intake pipe.
For example, a key switch actuates a solenoid for stopping a fuel injection pump, and which is disclosed in the Japanese utility model publication No. 61-167436 and No. 61-171843 (1986) as prior art.
According to the prior art disclosed above, the key switch must be kept in electrical contact with the accessory terminal until the diesel engine is stopped. However, it is easily forgotten to return the switch, so that the battery is unnecessarily charged.
In order to eliminate such inconvenience described above, there has been proposed a device to stop the engine by using timer means 1 as shown in FIG. 1, which is disclosed in detail in utility model publication No. 61-164441 (1986).
In this prior art device, a potential difference occurs in a diode bridge circuit 4 because a hydraulic switch 3 is ON during operation. A first NPN type transistor Tr1 turns on because of the connection between a key switch 2a and an OFF terminal during the engine stopping. An ON-operation causes a capacitor C1 to start charging and causes a PNP type transistor Tr2 and a second NPN type transistor Tr3 to turn on during the capacitor charging, so that current flows in an excitation coil 5 of a solenoid (not shown). As the solenoid operates a control rod of a fuel injection pump (neither shown) to return, the diesel engine stops because of cutting the fuel supply during a predetermined time of a time constant of the capacitor C1.
However, there remains some problems in the shut-down device of the prior art.
First, there is a problem that the capacitor C1 does not have enough time to restart the engine immediately after a stop because the capacitor C1 of the timer means 1 is fully charged immediately after the engine stops. It is therefore difficult to stop the engine again.
Second, there is a problem of interference caused at mounting a new battery to a vehicle when the battery 6 must be exchanged for a new one. Because the transistor Tr2 instantaneously turns on when new battery 6 is connected with vehicle electrical system and sparking occurs easily at the battery terminal. In this case, if the key switch 2 is turned off, a leak current occurs in the capacitor C1 and the battery 6 is discharged even when the engine stops.
Third, there is a problem of complex starting operation because the starter (not shown) must be operated until the oil pump pressure becomes high enough to turn on an oil pressure switch 3 when the necessary speed has been obtained after starting the engine.
Fourth, there is a problem of difficulty in starting the engine because of a current flowing in the excitation coil 5. Because the oil pressure switch 3 does not operate and because the first transistor Tr1 turns on despite there being no actual oil leak.
Last, there is a problem of a lowered reliability of products because of an increase in the number of causes of trouble. Since it is necessary to provide a diode bridge circuit 4 to detect the potential difference, the entire circuit is therefore more complex. Furthermore, the conventional shut-down device is suitable for general use.